title: Deflectometric analysis of high volume injection molds for production of occupational eye wear.
abstract: OBJECTIVE
  Most of the protective eye wear devices currently on the market are manufactured on simple polycarbonate shields, produced by injection molding techniques. Despite high importance of optical quality, injection molds are rarely inspected for surface quality before or during the manufacturing process. Quality degradation is mainly monitored by optical testing of the molded parts. The purpose of this work was to validate a non-contact deflectometric measurement technique for surface and shape analysis of injection molds to facilitate deterministic surface quality control and to monitor minor conformity of the injection mold with the design data.
  
  
  METHODS
  The system is based on phase-measuring deflectometry with a operating measurement field of 80×80 mm(2) (±18° slope), a lateral resolution of 60μm and a local sensitivity of some nanometers. The calibration was tested with a calibration normal and a reference sphere. The results were crosschecked against a measurement of the same object with a tactile coordinate measuring machine. Eight injection molds for production of safety goggles with radii of +58mm (convex) and -60mm (concave) were measured in this study. The molds were separated into two groups (cavity 1 and 2 of the tool with different polishing techniques) and measured to test whether the measurement tool could extract differences. The analysis was performed on difference height between the measured surface and the spherical model.
  
  
  RESULTS
  The device could derive the surface change due to polishing and discriminate between both polishing techniques, on the basis of the measured data. The concave nozzle sides of the first group (cavity 1) showed good shape conformity. In comparison, the nozzle sides of the second group (cavity 2) showed local deviations from design data up to 14.4μm. Local form variations of about 5μm occurred in the field of view. All convex ejector sides of both groups (cavity 1 and 2) showed rotational symmetric errors and the molds were measured in general flatter than design data.
  
  
  CONCLUSIONS
  We applied a deflectometric system for measuring and evaluating specular reflective injection molding tools to optimize the production process of occupational eye wear. The surface quality could be inline monitored in the production processes for actual spectacle models.
authors.affiliation: Experimental Ophthalmology, Saarland University, Kirrberger Straße 100, 66424 Homburg/Saar, Germany. Electronic address: alexis.speck@mx.uni-saarland.de.
authors.forename: Alexis
authors.initials: A
authors.lastname: Speck
authors.forename: Benedikt
authors.initials: B
authors.lastname: Zelzer
authors.forename: Marco
authors.initials: M
authors.lastname: Speich
authors.forename: Rainer
authors.initials: R
authors.lastname: Börret
authors.forename: Achim
authors.initials: A
authors.lastname: Langenbucher
authors.forename: Timo
authors.initials: T
authors.lastname: Eppig
mesh_terms: D019544:Equipment Failure Analysis / Q000379:methods*; D005135:Eye Protective Devices; D006245:Hardness Tests / Q000379:methods*; D007221:Industry / Q000295:instrumentation*; D013499:Surface Properties
keywords: 3D-Messung; 3D-measurement; Augenschutz; Deflektometrie; Fertigungsprozess; Safety goggles; Schutzbrillen; Spritzgießen; deflectometry; eye protection; injection molding; manufacturing